As a sign man for nearly 46 years, give or take a year or two (who can remember that far back?), the only time intelligent businesses use quotation marks in the USA in their signage is when it has been created, as a slogan, through newspaper, radio, or TV advertising. I always advise not using quotation marks if the quote is not well known, and if it has not been accepted through the media. Otherwise, it it will not be taken seriously.

On the subject of quote marks, the normal conventions in Britain (I can’t speak for Ireland) are indeed, in books, single quote marks for speech, with double quote marks for quotes-within-quotes; while for newspapers and magazines in general it’s the other way round, double quote marks for speech, with single quote marks for quotes-within-quotes, the main exception being The Observer, a national Sunday newspaper, which follows the book industry convention, even though its sister newspaper, the Guardian, uses the standard newspaper style (this is a complete PITA when, as I am, you’re only a once-in-a-blue-moon sub on the Obs and I have to try to reverse all my usual quotemark instincts).

One final wrinkle - in British newspaper headlines, picture captions and other “furniture”, the convention is for single quote marks, always, because they look better in larger type sizes ...

While we’re on about punctuation conventions, I remember seeing books printed in the first half of the last century using a single em dash (or something very much like it) for quotation of direct speech; e.g., Joyce’s Portrait of the Artist as a Young Man. German uses (or used to use) „ and ‟ and French « and » (or ‹ and ›) to delimit quoted text.